Analyte quantitation

1. A method for determining the quantity of at least one analyte in a sample, the method comprising: providing a lateral flow strip comprising a capture moiety and a conjugate comprising a detection moiety capable of binding the at least one analyte and highly-doped upconversion nanoparticles for visualising interaction of the at least one analyte and the capture moiety; applying the sample to the lateral flow strip such that the conjugate binds the analyte to provide a bound analyte that is subsequently captured by the capture moiety; providing a testing device comprising an excitation light source configured to elicita detectable signal from the highly-doped upconversion nanoparticles and a detector to capture the detectable signal, the testing device being capable of receiving the lateral flow strip; inserting the lateral flow strip to which the sample has been applied into the testing device; irradiating an area of the lateral flow strip comprising the highly-doped upconversion nanoparticles with a beam of light so as to elicit a detectable signal from the highly-doped upconversion nanoparticles; and detecting the detectable signal and determining the quantity of the at least one analyte in the sample based on the detectable signal, wherein the highly-doped upconversion nanoparticles comprise a host material, a sensitiser which is Yb3+ or Er3+, and an activator which is Er3+, Tm3+, or Ho3+, and wherein the sensitiser is present in a concentration of at least 30 mol % and the activator is present in a concentration of at least 3 mol %, or wherein the highly-doped upconversion nanoparticles comprise a host material and an activator which is Er3+ in a concentration of at least 50-8 mol %.

2. The method of claim 1, wherein the sensitiser is present in a concentration of 30 mol % to 80 mol %.

3. The method of claim 1, wherein the sensitiser is Yb3+.

4. The method of claim 1, wherein the host material is an alkali fluoride, an oxide or an oxysulfide.

5. The method of claim 4, wherein the host material is selected from the group consisting of: NaGdF4, Ca2F, NaYF4, LiYF4, NaLuF4, LiLuF4, KMnF3 and Y2O3, including combinations thereof.

6. The method of claim 1, wherein the highly-doped upconversion nanoparticles are inert shell passivated.

7. The method of claim 1, wherein the highly-doped upconversion nanoparticles are 8% Er/60% Yb@NaYF4, 8% Tm/60% Yb@NaYF4 or 40% Er/60% Yb@NaYF4 or 100% Er@NaYF4.

8. The method of claim 1, wherein the capture moiety and/or the detection moiety include one or more of: an antibody, an aptamer, an epitope, a nucleic acid or a molecular imprinted polymer.

9. The method of claim 1, wherein the testing device further comprises a lens or an array of lenses interposed between the excitation light source and the lateral flow strip so to focus the beam of light on the lateral flow strip, or wherein the testing device further comprises a lens or an array of lenses interposed between the lateral flow strip and the detector so as to focus the signal on the detector.

10. The method of claim 1, wherein the detector is a camera or a single element detector.

11. The method of claim 10, wherein the detector is a smart phone camera.

12. The method of claim 1, wherein the detectable signal is visible light or infrared light.

13. The method of claim 1, wherein the excitation light source is a laser diode or a near IR light source.

14. The method of claim 1, wherein the beam of light has a power density of at least about 0.001 MW/cm2.

15. The method of claim 1, wherein the area irradiated is between about 1 μm2 and about 10,000,000 μm2.

16. The method of claim 1, wherein the sample is a biological sample.

17. The method of claim 1, wherein the analyte is a biomarker.

18. The method of claim 1, wherein the method comprises determining the quantity of a plurality of analytes.

19. The method of claim 1, wherein the quantity of the at least one analyte in the sample is determined by fitting intensity of an image captured by the detector with a pre-set intensity-concentration curve for the analyte.